Embodiments of the present invention relate to wireless communications and in one embodiment power management of a radio transceiver in a wireless device such as a smart phone or a media player which includes a radio transceiver.
Data processing systems, such as general purpose computers or smart phones or media players often include a radio transceiver in order to allow wireless connectivity to a network or to other devices. An example of a wireless network is a network which complies with the WiFi standards, such as the IEEE 802.11 standards or other known standards, such as the WiMax standard, etc. The radio transceivers in the data processing systems can consume considerable power and hence quickly run down a battery in a mobile device to the point that the device can no longer be used. Efforts in the past to reduce battery consumption by a radio transceiver have involved placing the radio transceiver in a sleep state in which it consumes lower power. For example, the radio transceiver can be turned off or otherwise placed in a low power state in which many of the components of the radio transceiver consume little or no power. FIG. 1A shows an example of a prior device which includes a radio transceiver which can communicate to a wireless network, such as a WiFi network. The radio transceiver can be placed in a sleep state 12 in which it has a reduced power consumption. There is a sleep timer which periodically causes the system to turn on the radio to check to see if there are any messages or data pending to be received by the device. This periodic checking for data is shown as event 20. If no data is available to be received by the device, it goes back to sleep as shown by event 20 which loops back to the sleep state 12. At any point in time the device can decide to transmit data in which case it will exit the sleep state as is known in the art and enter the awake state 14. In typical implementations according to the WiFi standards, a device will awake from sleep to check availability of data at either every beacon (referred to in the WiFi standards as a Target Beacon Transmit Time (TBTT) or at every multiple of beacons which is referred to as a DTIM period (Delivery Traffic Indication Message). As shown by the state diagram 10 in FIG. 1A, an event which awakes the device from sleep is the event 16; this event occurs when the sleep timer expires and the radio transceiver determines from the beacon signal from a wireless access point that there is data pending or available at an access point to be received by the device. This causes the device to transition from sleep state 12 to awake state 14. At this transition, an awake timer is started and this timer, when it expires, causes the device to transition from the awake state 14 back to the sleep state 12. The device can receive data or transmit data while it is in the awake state. An optional transition (not shown) from the awake state 14 back to the awake state 14 can be used to reset the awake timer when data is received or transmitted. As is known in the art, the sleep timer in the sleep state causes the system to periodically wake up to determine whether data is available for it, and the awake timer will force the system, when there is no network activity, to go back to sleep.
FIG. 1B shows an example in the prior art of how a radio transceiver can be controlled in order to regulate power consumption while still allowing the system to communicate wirelessly to a wireless network or other device. A plurality of TBTTs are shown in time. These TBTTs include TBTT 27 and TBTT 29, each of which correspond to a particular DTIM. It can be seen that the radio was turned on during the period 32 and also during the period 34, each of which span slightly more than one interval between successive TBTTs. The device operating as shown in FIG. 1B will turn its radio on during period 32 to listen for activity and then turn it off after realizing there is no activity for it; in other words, the device turns on the radio just before a TBTT and turns off the radio just after the next successive TBTT as shown in FIG. 1B. In the case where a device is in sleep state 12, it can re-enter the sleep state immediately from event 20 if the device determines that there is no data pending at the access point and if the device has no data to send to the access point.
While these techniques to control power consumption do produce some savings in power consumed, there is often a need for further reduction in power consumption.